Molecular formulas Knowledge-Based Practice

Questions

1. 1.

   A sample containing $3.011 \times 10^{23}$ molecules of a compound with the empirical formula $\text{BH}_3$ has a mass of $13.84\text{ g}$. What is the molecular formula of this compound? (Atomic masses: $\text{B} = 10.81\text{ g/mol}$, $\text{H} = 1.01\text{ g/mol}$; Avogadro's number: $N_A = 6.022 \times 10^{23}\text{ mol}^{-1}$)

   • A) $\text{BH}_3$
   • B) $\text{B}_2\text{H}_6$
   • C) $\text{B}_3\text{H}_9$
   • D) $\text{B}_4\text{H}_{12}$
2. 2.

   A 0.0500 mol sample of a molecular compound contains 0.300 mol of carbon atoms, 0.600 mol of hydrogen atoms, and 0.100 mol of oxygen atoms. What is the molecular formula of the compound?

   • A) $\text{C}_6\text{H}_{12}\text{O}_2$
   • B) $\text{C}_3\text{H}_6\text{O}$
   • C) $\text{C}_3\text{H}_6\text{O}_2$
   • D) $\text{C}_6\text{H}_6\text{O}$
3. 3.

   A gaseous nitrogen oxide has the empirical formula $\text{NO}_2$. If a $0.200\text{ mol}$ sample of this gas has a mass of $18.4\text{ g}$, what is the molecular formula of the compound? (Atomic masses: $\text{N} = 14.01\text{ g/mol}$, $\text{O} = 16.00\text{ g/mol}$)

   • A) $\text{N}_2\text{O}_4$
   • B) $\text{NO}_2$
   • C) $\text{N}_2\text{O}_5$
   • D) $\text{N}_3\text{O}_6$
4. 4.

   A compound consists of 85.6% carbon and 14.4% hydrogen by mass and has an experimentally determined molar mass of 56.11 g/mol. What is the molecular formula of this compound? (Atomic masses: C = 12.01 g/mol, H = 1.01 g/mol)

   • A) $\text{CH}_2$
   • B) $\text{C}_2\text{H}_4$
   • C) $\text{C}_3\text{H}_6$
   • D) $\text{C}_4\text{H}_8$
5. 5.

   A compound has the empirical formula $\text{CH}_2\text{O}$ and a molar mass of 180.16 g/mol. What is its molecular formula? (Atomic masses: C = 12.01 g/mol, H = 1.01 g/mol, O = 16.00 g/mol)

   • A) $\text{C}_5\text{H}_{10}\text{O}_5$
   • B) $\text{C}_6\text{H}_{12}\text{O}_6$
   • C) $\text{C}_3\text{H}_6\text{O}_3$
   • D) $\text{C}_6\text{H}_6\text{O}_6$

Answers and step-by-step solutions appear after you finish the test.